1. Field of the Invention
The present invention generally relates to a method and an apparatus for treating organic liquid waste. More specifically, the present invention relates to a method and an apparatus for treating organic liquid waste using a biofilm.
2. Background Information
All of patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by references in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Organic-based liquid waste (hereinafter referred to as an organic liquid waste) is usually treated by an available method so that the treated liquid waste satisfies predetermined emission regulations before the treated liquid waste is then emitted from a factory. The term “organic liquid waste” is defined to be a liquid-state waste including at least one organic-based matter. A typical example of the organic liquid waste may include, but is not limited to, organic wastewater. The predetermined emission regulations include Biochemical Oxygen Demand (hereinafter referred to as BOD). BOD is a measure of the quantity of oxygen consumed by microorganisms such as aerobic bacteria during decomposition of organic matter in water. BOD may also be an index of water pollution. A higher level of BOD represents higher level of pollution in the water. A BOD component is a substance or matter that is subject to oxidation and decomposition by microorganisms, and is included in the organic liquid waste.
The BOD component in the organic liquid waste such as isopropyl alcohol (IPA) and tetramethyl ammonium hydroxide (TMAH) emitted in semiconductor manufacturing processes is oxidized and decomposed by a biofilm method and then discharged from the factory. In accordance with the biofilm method, the BOD component is oxidized and decomposed by a film of aerobic microorganisms that are adhered on a surface of a fixed bed in a reactor. The aerobic microorganisms consume oxygen to decompose the organic matter in the waste. It has been known that air-distribution manifolds are provided in the reactor for supplying oxygen to the aerobic microorganisms.
Japanese Laid-Open Patent Publication No. 5-261394 discloses a conventional method for treating the organic liquid waste. The conventional method utilizes a reservoir vessel, a wet catalyst tower for oxidation, a neutralization vessel, and a high pressure biofiltration vessel for treatment of the organic liquid waste.
The organic liquid waste is introduced into the reservoir vessel. The waste is then fed by a pump to the wet catalyst tower through a first feeding pipe, which connects the reservoir vessel to the wet catalyst tower. The pipe has a half-way connecting portion which is connected with a supplying pipe for supplying an oxygen-containing gas which has been pressurized by a compressor. The waste on the feeding through the pipe is mixed with the pressurized oxygen-containing gas at the half-way connecting portion. The wet catalyst tower has a catalyst bed which is formed by filling a catalyst into a high pressure container. The waste flows through the catalyst bed at a high temperature and under a high pressure, whereby the waste is oxidized. The oxidized waste is then subjected to pH-adjustment in the neutralization vessel. The pH-adjusted waste is then fed to the biofiltration vessel. The biofiltration vessel has a second feeding pipe for feeding the oxidized waste. The biofiltration vessel also has air-distribution manifolds. The biofiltration vessel further has a holder for holding particle-carriers that support microorganisms.
The oxidized waste is introduced through the second feeding pipe into the high pressure biofiltration vessel. The oxidized waste flows in proximity to the particle-carriers with a flow of the air supplied through the air-distribution manifolds. The oxidized waste is treated and filtrated with aerobic microorganisms in the form of a biofilm adhered on a surface particle-carriers, thereby removing the BOD component and CODCr component from the waste. COD means Chemical Oxygen Demand. The biofilm method feeds an organic matter to aerobic microorganisms for growth and multiplication thereof. The activity of microorganisms depends on oxygen, humidity, and nutrition. This means that the capacity of the organic liquid waste treatment apparatus depends on oxygen, humidity, and nutrition. Under atmospheric pressure, 8.8 mg/L of oxygen, which is fed to aerobic microorganisms, is dissolved in pure water. 8.8 mg/L is a maximum concentration at 20° C. A preferable temperature range for aerobic microorganisms to exhibit highest biological activity depends on the types or species of microorganisms. For example, 30-40° C. is preferable. Nitrogen and phosphorous as nutrition are supplied to the aerobic microorganisms at weight ratios of BOD:N:P=100:5:1.
The conditions for oxidation-decomposition reactions by the aerobic microorganisms include an amount of oxygen, humidity, and nutrition. The three conditions are important for the aerobic microorganisms to exhibit higher biological activity. In the conventional biofilm method, oxygen is dissolved in the organic liquid waste under atmospheric pressure. However, just 5-6% of oxygen can be dissolved in the organic liquid waste. Lower concentrations of oxygen dissolved in the organic liquid waste cause the aerobic microorganisms to exhibit lower biological activity.
In accordance with the conventional biofilm method, 1 m3 of the biofilm decomposes approximately 1-2 kg of the BOD component per day even if the temperature and the nutrition are optimized. No higher efficiency of the decomposition can be obtained using a conventional biofilm method. A large scale biofilm reactor is required for containing a large amount of microorganisms. A large space is thus required for installing the reactor.
The conventional method disclosed in the above-mentioned Japanese publication is to oxidize the organic liquid waste with a wet catalyst at a high temperature under a high pressure before the biofilm reactor decomposes the BOD component, which mainly includes a residual organic acid having a low molecular weight. Not only the biofiltration chamber but the wet catalyst tower is required, which shares a large area and requires a high cost.
Air is introduced into the biofilm reactor through the air-distribution manifolds. A uniform supply of oxygen throughout an inner space of the biofilm reactor requires a number of the air-distribution manifolds provided in the biofilm reactor. Each of the air-distribution manifolds has plural oxygen-injection holes that are aligned along an air stream direction. This makes it difficult to realize a desired uniform injection of oxygen from the plural oxygen-injection holes.
Further, sludge of dead microorganisms may block some of the oxygen-injection holes, resulting in a non-uniform oxygen supply to the reactor. This causes a variation in biological activity of microorganisms with a position in the inner space of the reactor. The variation drops the total efficiency of oxidation-decomposition by the biofilm.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved a method and an apparatus for treating an organic liquid waste. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.